1. This work was supported by NASA grants: Wind grant NNX13AP39G and Cluster grant NNX11AH03G. Motivating Questions Observational Study of Ion Diffusion Region Tailward of the Cusp: Cluster Observations in 2001-2008 F.M. Muzamil 1 (fmt7@wildcats.unh.edu), C.J. Farrugia 1, R.B. Torbert 1 1 Space Science Center, University of New Hampshire, Durham, NH, USA. We focus on one specific area; Reconnection Poleward of the Cusp (POC). Large range of density asymmetries (N Asym ) and guide fields (B G ) are surveyed Surveyed 8 yrs of magnetopause (MP) crossings at high latitudes POC by Cluster o 16 crossings of the Ion Diffusion Region (IDR) o Wide range of Density asymmetries (~10 to 103) Magnetic field asymmetries (~0.2 to 0.9) Guide fields (~5% to 65%) Emphasis is on Observations: Focus on o Effect of N Asym o Effect of N Asym + B G on the 2D IDR structure 3 case studies (including limiting cases) What is a “small”, “moderate”, “large” N Asym ? What is a small B G vs. moderate B G ? At what value of the N Asym /B G do the features of the IDR start to deviate from features observed in symmetric reconnection? How can we compare in-situ observations against current theory and simulations? References Acknowledgements We examined in situ data to investigate the structure of 2D reconnection layer for Poleward of the Cusp (POC) a wide range of NAsym and BGs Found numerous crossings with NAsym up to 3 orders of magnitude Worthwhile to conduct numerical simulations with a higher density asymmetry than usually done Measured values of the outflow velocity and density in POC observations are in good agreement with expectations and theory Analysis of the separation of the X line and Stagnation line are being conducted Summary + Conclusions Borovsky, J. E., and M. Hesse (2007), Phys. Of Plasmas, 14, 102309, 2007 Cassak, P. A., and M. A. Shay, Phys. Of Plasmas, 14, 102114, 2007 Cassak, P. A., and M. A. Shay, Phys. Of Plasmas, 16, 055704, 2009 Eastwood, J.P., T. D. Phan, M. Øieroset, and M. A. Shay, 115, A08215, JGR, 2010a Eastwood, J. P., M. A. Shay, T. D. Phan, et al., PRL, 104, 205001, 2010b Levy, R. H., H. E. Petschek, and G. L. Siscoe, AIAA J., 2, 2065, 1964 Lybekk, B., A. Pedersen, S. Haaland, et al., JGR, 117, A01217, 2012 Mozer et al., PRL, 89, 015002, 2002 Mozer, F. S., P. L. Pritchett, et. al., JGR, 113, A00C03, 2008 Muzamil, F. M., Farrugia, C. J., et al., JGR, 119, A019879, 2014 Pritchett, P.L., JGR, 113, A06210, 2008, Pritchett, P. L., and F. S. Mozer, JGR, 114, A11210, 2009 Scudder, J. D., R. D. Holdaway, et. al., JGR, 113, A10208,2008 Tanaka, K. G., et al., Ann. Geophys., 26, 2471–2483, 2008 Twitty, C., T. D. Phan, G. Paschmann, et. al., GRL, 31, L19808, 2004 Wang, S., L. M. Kistler, et. al., JGR, 120, A021524, 2015 Observations: Range of N A symm & B G covered Ability compare the effect of B G for a range of N Asym N Asym for a range of B G No absolute criterion for identifying the IDR Plausible arguments for IDR identification 1a. Sharp reversal of flow direction in the middle of the crossing 1b. Correlated reversal in V X and B Z (V L and B N ) 2a. E+(V i × B) ≠0 for ions but E+(V e × B) =0 for electrons 2b. Adiabatic expansion parameter, δi > 1 3. Peak values of the total DC electric field > several tens mV/m 4. Deep minimum in total B 5. Existence of expected Hall field Features Adopted a confidence level 1-3 depending on how many criteria were fulfilled Assumptions : B 1 and B 2 are antiparallel/ No guide field Cassak and Shay et al. 2007, 2009 Theoretical Scaling Relations MSP MSH C3 N Asym 8.6 B Asym 0.5 BGBG -13 nT (62%) Quadrupolar B M structure is still preserved, although there is a small density asymmetry However, B M is asymmetric Bi polar E N feature is asymmetric Reversal in Hall fields, B M and E N, does not occur at the center of the CS Similar effect was seen by Eastwood et. al., [2010b] in a magnetotail event for no density asymmetry (N Asym = 1) and B G = 20% Muzamil, Farrugia et al. 2016, submitted Hall Fields C3 N Asym 25 B Asym 0.58 BGBG 0.85 nT (4%) NiNi TiTi BLBL BMBM BNBN B VLVL VMVM VNVN V C3 N Asym 1300 B Asym 0.54 BGBG 22 nT (56%) MSH MSP X Outline We presented 3 case studies with different B G and N Asym to study the features of the 2D IDR. All 3 cases had very similar B Asym. For a small N Asym of ~9 the Hall B fields was still quadrupolar For a very large B G of 60%, Hall B field was asymmetric about the B L reversal and not centered at the CS crossing For a moderate N Asym of ~25 we observed bipolar Hall fields For a very small B G of 4%, the effect was negligible since the normalized Hall B field was symmetric For a very large N Asym of ~ 1300 we found a well define S line (slow expansion fan) where the flow velocity goes to 0 during a very sharp density gradient. X line and S line are separated very clearly which is an effect of the very large density asymmetry IDR Identification Jet #1 B M is negative during sunward jet Jet #2 B M is positive during anti-sunward jet Hall B field is symmetric for very small guide field Case Study 1 Case Study 2 Case Study 3 Earth’s Magnetoshpere Case Study 1: Small N Asym + Large B G Case Study 2: Moderate N Asym + Small B G Conclusions Case Study 3: High N Asym +Moderate B G